The background of the invention will be discussed in two parts;
1. Field of the Invention
This invention relates to laser apparatus and methods, and more particularly to a method and apparatus for engraving smoke-sensitive materials, such as paper, cloth and the like.
2. Description of the Prior Art
Laser engraving or cutting of items such as wood is well known to those skilled in the art. When wood items are engraved, normally a template made of brass is placed over the item, the template having openings therein in the form of the image or pattern to be engraved on the surface of the wood. The pattern is formed by chemical etching to remove the brass in the area desired. The template is provided with a peripheral frame which fits snugly about the wood item with the template in abutting relation with the surface to be etched or engraved by the laser beam. The laser beam, properly focused, is then scanned over the combination of the template and wood in some overlapping pattern so that there is relatively uniform coverage of the open areas in the brass template.
In such apparatus, it is usual to use a carbon dioxide laser having a power output in excess of 100 watts, with the beam being focused to a spot size intense enough to vaporize the wood to a given depth. Usually, power densities in excess of 30,000 watts per square centimeter are reached at or near the focus of the laser beam so that the wood can be cleanly vaporized. When vaporization occurs, the wood vapors escape from the part at high velocity. However, there is still condensation of these vaporized wood by-products on the surface of the wood and on the template. Usually, air flow prevents condensation of these vaporized wood by-products from taking place on the focusing lens or optics of the laser apparatus. When wooden items are engraved, the condensed vaporized wood by-products, or condensed smoke, can be cleaned from the wood item and from the template after the engraving is complete.
However, the above-described process and apparatus is not readily usable with thin, flexible, smoke-sensitive materials, such as paper and cloth, particularly where the laser is used to cut through the thin material, and more especially so when multiple sheets of the material are stacked to cut through several sheets or layers simultaneously.
For example, if multiple sheets of paper are stacked, and placed below a standard brass template and scanned with a laser beam several undesirable phenomena occur due to the smoke-sensitive and thermal-sensitive nature of the work piece. During the cutting process, the vaporized paper residue condenses on both sides of the paper along the cut edge, this deposit occurring on every sheet in the stack. This deposit has a brown tarnishing appearance and is somewhat sticky. In addition, this sticky residue deposits itself on the undersurface of the template, causing adherence of the top sheet of paper to the template adjacent the cut edge. It is uneconomical to remove the deposit from the sheets of paper, thus rendering this process unsuitable for cutting paper in stacked layers.In addition, with stacked sheets of paper, the paper near the top of the stack goes through dimensional changes as the lower sheets are cut due to the intense heat involved. Due to these thermal effects, and the dimensional changes, there is movement of the upper sheets of paper, which causes the openings formed therein to increase in size to the extent that many fine lines, which are intended to be left as strips of paper, are in fact, eliminated.
It is an object of the present invention to provide a new and improved apparatus and method for laser cutting of paper, or similar thin smoke-sensitive material.
It is another object of the present invention to provide a new and improved method and apparatus for laser cutting of a stack of sheets of material, such as paper or the like.
It is still another object of the present invention to provide a new and improved process and apparatus for laser cutting of cloth of different compositions.